The present invention is a catalyst for the hydrogenation of unsaturated organic compounds and a process that uses the catalyst and can be carried out at low temperatures and pressures. More specifically, the invention relates to a process for the hydrogenation of ketones and aldehydes to alcohols using organometallic tungsten (W) and molybdenum (Mo) complexes as catalysts.
Hydrogenation reactions involve the addition of hydrogen to an organic compound whereby, for example, a ketone can be reduced to an alcohol. Prior art processes have generally required the presence of a heterogeneous catalyst with a solid phase of platinum, rhodium, palladium or nickel along with relatively high hydrogen pressure and elevated temperature.
Traditional homogeneous catalysts for hydrogenation of ketones or aldehydes use precious metals such as rhodium (Rh), iridium (Ir) or ruthenium (Ru), which are extremely expensive and, therefore, frequently uneconomical. In contrast, the catalysts of the present invention, which use either molybdenum (Mo) or tungsten (W), are much less expensive to prepare, and, thus, offer economic advantages.
The present invention provides a catalyst and a process that uses the catalyst for the homogeneous catalytic hydrogenation of ketones to alcohols with H2 as the stoichiometric redundant and organometallic tungsten (W) and molybdenum (Mo) complexes as the catalysts.
The present invention is a catalyst and a process for the catalytic hydrogenation of an organic compound that contains at least one reducible functional group. The catalyst and the process are particularly well suited to the hydrogenation of ketones and aldehydes. The functional group is selected from groups represented by the formulas R*(Cxe2x95x90O)Rxe2x80x2 and R*(Cxe2x95x90O)H, wherein R* and Rxe2x80x2 are selected from hydrogen (H) or any alkyl or aryl group. R* and Rxe2x80x2 can both be selected from H or from an alkyl group or from an aryl group, and can be the same or different.
The process includes reacting the organic compound in the presence of hydrogen and a catalyst to form a reaction mixture. The catalyst includes a metal hydride and is prepared by reacting Ph3C+Axe2x88x92 with the metal hydride. Axe2x88x92 represents an anion and can be BF4xe2x88x92, PF6xe2x88x92, CF3SO3xe2x88x92 or BArxe2x80x24xe2x88x92, wherein Arxe2x80x2=3,5-bis(trifluoromethyl)phenyl.
The metal hydride is represented by the formula:
HM(CO)2[xcex75:xcex71xe2x80x94C5H4(XH2)nPR2]xe2x80x83xe2x80x83(1)
wherein M represents a molybdenum (Mo) atom or a tungsten (W) atom; X is a carbon atom, a silicon atom or a combination of carbon (C) and silicon (Si) atoms; n is any positive integer, preferably between 1 and 6; R represents two hydrocarbon groups selected from H, an aryl group, an alkyl group or a combination thereof, the preferred hydrocarbon groups are a cyclohexyl group (C6H11), a methyl group (CH3), a phenyl group (C6H5) and a tert-butyl (tBu) system. Both R groups can be the same or different. The metal hydride is reacted with
Ph3C+Axe2x88x92xe2x80x83xe2x80x83(2)
either before reacting with the organic compound or in the reaction mixture.
In one embodiment, the catalyst is prepared by reacting the metal hydride with Ph3C+Axe2x88x92 in the reaction mixture and the anion (Axe2x88x92) is BF4xe2x88x92, PF6xe2x88x92, or BArxe2x80x24xe2x88x92, wherein Arxe2x80x2=3,5-bis(trifluoromethyl)phenyl. In another embodiment, the catalyst is prepared by reacting the metal hydride with Ph3C+Axe2x88x92 prior to reacting with the organic compound and the anion (Axe2x88x92) is CF3SO3xe2x88x92.
The catalysts have a bridge made up of a carbon group (CR2), a silicon group (SiR2) or a combination of carbon and silicon groups that connect the cyclopentadienyl ligand (xe2x80x94C5H4) to the phosphine ligand (PR2) of the metal hydride. The carbon/silicon bridge connects the cyclopentadienyl ligand (xe2x80x94C5H4) to the phosphine ligand (PR2) of the metal hydride.
The process is carried out in the presence of hydrogen at a pressure of from 0.5 atmosphere to 5,000 psi, preferably at a pressure of from 1 atmosphere to 100 psi, and at a temperature of from 0xc2x0 C. to 100xc2x0 C.
The molybdenum and tungsten catalyst complexes of the present invention provide significant cost advantages over prior art processes, which use expensive rhodium, iridium and ruthenium catalyst complexes. The less expensive catalysts of the present invention make it practical to hydrogenate organic compounds in commercial operations that previously had not been economically feasible.
Hydrogenation processes that are currently in use employ Mo and W (inexpensive metals) to hydrogenate ketones under mild conditions of temperature and pressure. However, a limitation encountered with these processes is the decomposition of the catalysts, due to dissociation of a phosphine ligand. The present invention provides catalysts with significantly higher lifetimes and increased thermal stability. Moreover, the homogeneous organometallic Mo and W complexes of the present invention provide an effective hydrogenation catalyst at a considerably reduced cost over the prior art catalysts that use Rh (rhodium), Ir (iridium) or Ru (ruthenium) complexes.